Spontaneous self-assembly of aromatic cyclic dipeptide into fibre bundles with high thermal stability and propensity for gelation

Cyclic dipeptides (CDPs) are the simplest members of cyclic peptides exhibiting exceptional rigidity and stability. A detailed study on the spontaneous self-assembly of aromatic CDP (Phe-Phe) into fibre bundles with 1–2 μm thick and several millimetres long is described. These fibre bundles exhibit the structural hierarchy that is found in natural fibres such as spider silk and collagen. The solubility studies in various solvents provided more insights into the existence and nature of fibre bundles. Fibre bundles transform to gel in chloroform at critical concentration of added trifluoroacetic acid. Thermogravimetric analysis data indicated high thermal stability with multiple transitions attributed to the existence of structural hierarchy in fibre bundles. NMR studies revealed that aromatic π–π interactions along with intermolecular (N–H…O) hydrogen-bonded molecular chains are mainly responsible for the formation as well as observed high stability of fibre bundles. This detailed study of structural hierarchy, solubility, gelation and thermal stability demonstrates the robustness of aromatic CDP (Phe-Phe) to form fibre bundles.     

A series of lanthanide-transition metal frameworks based on 1-, 2-, and 3D metal-organic motifs linked by different 1D copper(I) halide motifs

Hydrothermal reactions of lanthanide(III) oxide and copper halide with isonicotinic acid (Hina) and pyridine-2,3-dicarboxylic acid (H2pdc) or 1,2-benzenedicarboxylic acid (H2bdc) lead to three novel lanthanide(III)-copper(I) heterometallic compounds, namely, [Ce2(ina)5(na)2(H2O)2][Cu5Br4] (1, na=nicotinic acid), [Er4(ina)8(bdc)2(OH)(H2O)5][Cu8I7] (2), and [Ce3(ina)8(bdc)(H2O)4][Cu7Br6] (3). Compound 1 is constructed from two distinct units of the Ln-organic double chains and inorganic [Cu5Br4]nn+ chains. Compound 2 consists of 2D Ln-organic layers and 1D [Cu8I7]nn+ cluster chains. Compound 3 can be viewed as a 1D [Cu6Br6]n chainlike motif inserted into the channels of a 3D Ln-Cu-organic motif. Compounds 1-3 exhibit three different 1D inorganic copper(I)-halide chains interconnected with metal-organic 1D chains, 2D layers, and 3D nets resulting in three mixed-motif non-interpenetrating heterometallic Cu-halide-lanthanide (Ln)-organic frameworks, which represent good examples and a facile method to construct such mixed-motif heterometallic compounds. Furthermore, the IR, TGA, and UV-vis spectra of 1-3 were also studied.     

Effect of surface modes on the six-dimensional molecule-surface scattering dynamics of H2-Cu(100) and D2-Cu(111) systems

We include the phonon modes originating from the three layers of Cu(100)/Cu(111) surface atoms on the dynamics of molecular [H(2)(v,j)/D(2)(v,j)] degrees of freedom (DOFs) through a mean field approach, where the surface temperature is incorporated into the effective Hamiltonian (potential) either by considering Boltzmann probability (BP) or by including the Bose-Einstein probability (BEP) factor for the initial state distribution of the surface modes. The formulation of effective potential has been carried out by invoking the expression of transition probabilities for phonon modes known from the "stochastic" treatment of linearly forced harmonic oscillator (LFHO). We perform four-dimensional (4D?2D) as well as six-dimensional (6D) quantum dynamics on a parametrically time and temperature-dependent effective Hamiltonian to calculate elastic/inelastic scattering cross-section of the scattered molecule for the H(2)(v,j)-Cu(100) system, and dissociative chemisorption-physisorption for both H(2)(v,j)-Cu(100) and D(2)(v,j)-Cu(111) systems. Calculated sticking probabilities by either 4D?2D or 6D quantum dynamics on an effective potential constructed by using BP factor for the initial state distribution of the phonon modes could not show any surface temperature dependence. In the BEP case, (a) both 4D?2D and 6D quantum dynamics demonstrate that the phonon modes of the Cu(100) surface affect the state-to-state transition probabilities of the scattered H(2) molecule substantially, and (b) the sticking probabilities due to the collision of H(2) on Cu(100) and D(2) on Cu(111) surfaces show noticeable and substantial change, respectively, as function of surface temperature only when the quantum dynamics of all six molecular DOFs are treated in a fully correlated manner (6D).     

Asymmetrical polar modification of a bivanadium-capped Keggin POM by multiple Cu-N coordination polymeric chains

An unprecedented asymmetrically modified bivanadium-capped Keggin polyoxometalate (POM), {AsMo12O40(VO)[VO(H2O)]}.[Cu(4,4'-bipy)]5.H2O (1) (bipy = bipyridine), has been hydrothermally synthesized and structurally characterized by a routine technique. Single-crystal X-ray diffraction analysis reveals that compound 1 exhibits a unique (3,4,6)-connected 3D framework with a (6(2).8(1))2(8(3))2(6(4).8(2))2(6(1).8(14)) topology, constructed from {AsMo12O40(VO)[VO(H2O)]}5- polyoxoanions modified by six {Cu(bipy)}n coordination polymeric chains. The asymmetrical polar coordination mode has never been found in the POM chemistry hitherto. It is also the first example of the bivanadium-capped POM as an anionic template to construct a 3D framework with the highest connection number of bicapped POMs. Additionally, by just changing the length of the organic ligand, a new compound {[AsMo12O40(VO)2][Cu(bpe)]2}.[Cu(bpe)].[H2bpe].H2O (2) (bpe = bis(4-pyridyl)ethylene), has been obtained, in which the {AsMo12O40(VO)2} sections are modified by double monotrack {Cu(bpe)}n coordination polymeric chains to form a "rail-like" 1D structure.     

First three-dimensional inorganic-organic hybrid material constructed from an "inverted Keggin" polyoxometalate and a copper(I)-organic complex

A new polyoxometalate (POM) based on a flexible bidentate ligand and "inverted Keggin" inorganic building block, namely, [Cu(8)L(8)[Mo(12)O(46)(AsPh)(4)](2)]·H(2)O (1), where L is 1,3-bis(1,2,4-triazol-1-yl)propane, has been synthesized under hydrothermal condition. In 1, the "inverted Keggin" [Mo(12)O(46)(AsPh)(4)](4-) building blocks are linked by the one-dimensional (1D) zigzag [Cu(I)(trans-L)](+) chains and [Cu(I)(4)(cis-L)(4)](4+) macrocycles to yield a three-dimensional (3D) framework. The compound 1 represents the first 3D "inverted Keggin" polyoxometalate modified by a transition-metal complex. Topologically, the 3D framework can be considered as an 8-connected net with a Schl?fli symbol of 4(22)·6(6). As far as we know, compound 1 is the highest-connected uninodal network topology presently known for POM-based materials. The compound was characterized by its IR spectrum, UV-vis spectrum, thermogravimetric analysis (TGA), and powder X-ray diffraction (XRD) patterns. Remarkably, compound 1 exhibits photocatalytic activity for dye degradation under visible light irradiation and shows good stability toward visible-light photocatalysis.     

Tailoring Large Pores of Porphyrin Networks on Ag(111) by Metal–Organic Coordination

The engineering of nanoarchitectures to achieve tailored properties relevant for macroscopic devices is a key motivation of organometallic surface science. To this end, understanding the role of molecular functionalities in structure formation and adatom coordination is of great importance. In this study, the differences in formation of Cu‐mediated metal–organic coordination networks based on two pyridyl‐ and cyano‐bearing free‐base porphyrins on Ag(111) are elucidated by use of low‐temperature scanning tunneling microscopy (STM). Distinct coordination networks evolve via different pathways upon codeposition of Cu adatoms. The cyano‐terminated module directly forms 2D porous networks featuring fourfold‐coordinated Cu nodes. By contrast, the pyridyl species engage in twofold coordination with Cu and a fully reticulated 2D network featuring a pore size exceeding 3 nm² only evolves via an intermediate structure based on 1D coordination chains. The STM data and complementary Monte Carlo simulations reveal that these distinct network architectures originate from spatial constraints at the coordination centers. Cu adatoms are also shown to form two‐ and fourfold monoatomic coordination nodes with monotopic nitrogen‐terminated linkers on the very same metal substrate—a versatility that is not achieved by other 3d transition metal centers but consistent with 3D coordination chemistry. This study discloses how specific molecular functionalities can be applied to tailor coordination architectures and highlights the potential of Cu as coordination center in such low‐dimensional structures on surfaces.     

β-Loop, γ-loop,and helical peptide conformations in cyclopeptides containing a steroidal pseudo-amino acid

The steroidal pseudo-amino acids 3ã-amino-5β-cholan-24-oic acid ( 2a ), 12ã-acetoxy-3ã-ammonia-5β-cholan-24-oic acid ( 2b ), and 7ã,12ã-diacetoxy-3ã-amino-5β-cholan-24-oic acid ( 2c ) are used as rigid spacers in the backbone of the cyclic peptides cyclo(– 2a –Phe-Phe–)₂ ( 1a ), cyclo(– 2b –Phe-Phe–)₂ ( 1b ), and cyclo(–2c-Phe-Phe–)₂ ( 1c ). A homogeneous β-loop conformation is found in the peptide chains of 1a and 1b , while 1c exists as a mixture of ã-helical and γ-loop conformations. The structure and homogeneity of the conformations are established by several NMR techniques and are supported by molecular-dynamics calculations. The peptide conformations depend on the distance and attraction of the two large and lipophilic steroidal parts of the cyclic molecules.     

Synthesis, crystal structures and magnetic properties of Cu(II) compounds bridged by the terephthalate ligand and hydrogen bonds

A 3D network [Cu(tmen)(tp)(H₂O)₂]_n (1) (tmen = N,N,N′,N′-tetramethylethylenediamine; tp = terephthalate) and a 2D sheet [Cu(pyrazole)₂(tp)]_n (2), featuring 1D chains interwoven by hydrogen bonds, have been prepared and characterized by means of X-ray analyses and magnetic measurements. For 1, coordinative zigzag chains contain Cu(II) centers capped by the chelate ligand tmen, in which the tetragonal structure is elongated due to Jahn–Teller distortion. Coordinated water molecules are hydrogen-bonded to two free carboxylate oxygens of tp bridges, leading to the observed 3D structure. The use of the non-chelating capping ligand pyrazole produced the covalent-bonded 1D linear compound 2 with hydrogen bonds. A severe octahedral distortion of the Cu(II) center arises from a small bite angle (52.3(1)°) of two carboxylate oxygen atoms of tp, which are in turn hydrogen-bonded to the N–H groups of pyrazole ligands coordinated to Cu(II) atoms in neighboring chains. Magnetic data were fitted with the high-temperature series expansion for the Heisenberg chain spin Hamiltonian H = −J∑_iS_i · S_i + 1 together with consideration of the molecular field approximation (zJ′). Both compounds interestingly exhibit ferromagnetic interactions with g = 2.17, J = 4.08 cm⁻¹, zJ′ = −0.28 cm⁻¹ for 1 and g = 2.09, J = 1.47 cm⁻¹, zJ′ = −0.04 cm⁻¹ for 2. By taking into account structural parameters of distances between Cu atoms, it is reasonably assigned that the ferromagnetic couplings (J > 0) in these systems originate from the hydrogen bonds. The spin density of the d_x²-y² orbital on a Cu(II) atom in a chain is propagated and induced over the d_z² orbital of another Cu(II) atom in an adjacent chain. This orbital orthogonality gives rise to such interactions. The negative zJ′ term suggests that the tp bridges communicate only tiny antiferromagnetic interactions.     

4,4'-Bipyridazine: a new twist for the synthesis of coordination polymers

A new polydentate ligand 4,4'-bipyridazine (4,4'-bpdz) was prepared by employing inverse electron demand cycloaddition of 1,2,4,5-tetrazine. A unique combination of structural simplicity, ampolydentate character and efficient donor properties towards Cu(I), Cu(II) and Zn(II) provide wide new possibilities for the synthesis of coordination polymers incorporating the 4,4'-bpdz module either as a bi-, tri- or tetradentate connector between the metal ions. 1D coordination polymers Cu(2)(4,4'-bpdz)(CH(3)CO(2))(4) x 4H(2)O and Zn(4,4'-bpdz)(NO(3))(2), and interpenetrated (4,4)-nets in [Cu(4,4'-bpdz)(2)(H(2)O)(2)]S(2)O(6) were closely related to 4,4'-bipyridine compounds. 1D "ladder-like" polymer Cu(2)(4,4'-bpdz)(3)(CF(3)CO(2))(4) and the unprecedented 3D binodal net ({8(6)}{6(3);8(3)}) in [Cu(3)(4,4'-bpdz)(6)(H(2)O)(4)](BF(4))(6) x 6H(2)O were based upon a combination of linear and angular organic bridges. Complex [Cu(3)(OH)(2)(4,4'-bpdz)(3)(H(2)O)(2){CF(3)CO(2)}(2)](CF(3)CO(2))(2) x 2H(2)O has a "NbO-like" 3D topology incorporating discrete dihydroxotricopper(II) clusters linked by tri- and tetradentate ligands. The tetradentate function of the 4,4'-bpdz ligand was especially relevant for copper(I) complexes, which adopt layered Cu(2)X(2)(4,4'-bpdz) (X = Cl, Br) or 3D chiral framework (X = I) structures based upon infinite (CuX)(n) chains. The electron deficient character of the ligand was manifested by short anion-pi interactions (O-pi 3.02-3.20; Cl-pi 3.35 A), which may be involved as a factor for controlling the supramolecular structure.     

Construction of a porous homochiral coordination polymer with two types of Cu(n)I(n) alternating units linked by quinine: a solvothermal and a mechanochemical approach

The polymer network: The reaction of quinine (QN) with CuI under solvothermal, as well as liquid-assisted grinding, conditions afforded a unique 1D homochiral coordination polymer {[Cu(4)(μ(3)-I)(4)(QN)(2)][Cu(3)(μ(3)-I)(2)(μ(2)-I)(QN)(2)](2)}(n), containing both triangular Cu(3)I(3) and cubane Cu(4)I(4) clusters as connecting nodes (see scheme). Van der Waals interactions between the adjacent 1D polymer chains lead to an extended quasi-honeycomb homochiral pillared 3D network with solvent-free 1D channels.     

New organically templated copper(I) sulfites: the role of sulfite anion as both soft and hard ligand

Two new organically templated layered copper(I) sulfites, namely, {H2pip}{Cu3(CN)3(SO3)} (1) and {H2pip}{NaCu2(SO3)2Br(H2O)}.2H2O (2) (pip = piperazine), have been synthesized by hydrothermal reactions of copper(I) cyanide or copper(I) bromide with NaHSO3 and piperazine. Both compounds exhibit a layered structure. The 2D layer of {Cu3(CN)3(SO3)}2- in 1 is composed of 1D chains of copper(I) cyanide interconnected by sulfite anions via both Cu-S and Cu-O bonds, whereas the 2D layer of {NaCu2(SO3)2Br}2- in 2 is formed by 1D chains of copper(I) bromide and 1D sodium(I) aqua chains that are interconnected by sulfite anions via Na-O, Cu-S, and Cu-O bonds. Chemical bonding in 1 and 2 has been also investigated by theoretical calculations based on DFT methods.     

Copper(II), zinc(II), and cadmium(II) coordination polymers with 2-methylglutarato and 4,4′-dipyridyldisulfide

Three new coordination polymers of copper(II), zinc(II) and cadmium(II), Cu(H₂O)(Dpds)(2-MGA) (I), [Zn(Dpds)(2-MGA)] · 1.25H₂O (II) and [Cd(H₂O)(Dpds)(2-MGA)] · 0.25H₂O (III) (Dpds = 4,4′-dipyridyldisulfide, H₂MGA = (RS)-2-methyl glutaric acid), have been synthesized and characteried by X-ray single crystal structure determination. The Cu atoms in I are alternately bridged by Dpds ligands and 2-methylglutarato ligands to generate 1D chain. The resulted chains are assembled via S...S weak interactions into 2D layers, which are through twofold 2D parallel/2D parallel mode inclined interpenetration to induce 3D supramolecular architecture. In II, the ZnN₂O₂ tetrahedras are bridged by 2-MGA anion and Dpds ligands to form 2D (4,4) networks, which are assembled via hydrogen bonds to 3D supramolecular architecture. The centrosymmetric binuclear units Cd₂(2-MGA)₂ in III are bridged by Dpds ligands to form 1D repeated rhomboids chains, which are interlinked via S...S weak interactions into 2D layer, and the resulting 2D sheets are inclined parallel into 3D network.     

5-氨基双四唑富氮配位化合物的合成、结构及其对高氯酸铵的热分解影响

水热条件下合成了两个5-氨基双四唑配位化合物Cu(bta)(bpy)(H2O)(1)和Pb2(bta)2(en)2.4H2O(2)(H2bta=5-氨基双四唑,bpy=2,2′-联吡啶,en=乙二胺),并借助单晶X-射线衍射技术对其结构进行了表征。在配合物1中,5-氨基双四唑配体以双齿螯合模式与铜离子配位形成离散的分子,并通过H键作用进一步形成了三维的超分子结构。在配合物2中,强的R22(8)氢键环作用将双核的Pb2(bta)2(en)2单元连接成一维的链,这些链通过与水分子氢键作用被进一步组装成三维的超分子结构。另外,通过DSC技术探究了它们作为添加剂对高氯酸铵的热分解催化影响。研究发现,铅基化合物2的催化效果较铜基化合物1要好。     

Bis(o-phenylenebis(acetylacetonato))dicopper(II): a strained copper(II) dimer exhibiting a wide range of colors in the solid state

The bis(β-diketone) o-pbaH(2) (o-phenylenebis(acetylacetone), 1) reacts readily with Cu(2+). Although this reaction was expected to yield a trimeric product (2) on geometric grounds, the binuclear complex Cu(2)(o-pba)(2) (3) is obtained instead. Materials containing Cu(2)(o-pba)(2) adopt a variety of colors, depending on the solvents used in preparation: dark green (microcrystalline, 3a), golden-brown (ansolvous, 3b), green-brown (CHCl(3)-C(6)H(6) solvate, 4), dark blue (nitrobenzene solvate, 5), or violet (toluene solvate, 6). Complexes 5 and 6 contain 1D chains of Cu(2)(o-pba)(2) molecules joined by weak Cu···O interactions. Crystalline adducts [Cu(2)(o-pba)(2)L](n) (7 and 8) containing 1D polymeric chains are also obtained upon reaction of 3 with bridging ligands (L = 1,2-bis(4-pyridyl)ethane or 4,4'-bipyridine, respectively). All of the new metal complexes except for 3a have been characterized by X-ray analysis.     

Novel dinuclear and polynuclear copper(II)-pyrazine-2,3-dicarboxylate supramolecular complexes with 1,3-propanediamine, N,N,N′,N′-tetramethylethylenediamine and 2,2′-bipyridine

Three novel Cu(II)-pyrazine-2,3-dicarboxylate complexes with 1,3-propanediamine (pen), [Cu₂(μ-pzdc)₂(pen)₂] · 2H₂O (1), N,N,N′,N′-tetramethylethylenediamine (tmen), {[Cu(μ-pzdc)(tmen)] · H₂O}_n(2), and 2,2′-bipyridine (bipy), {[Cu(μ-pzdc)(bipy)]·H₂O}_n(3) have been synthesized and characterized by means of elemental and thermal analyses, magnetic susceptibilities, IR and UV/vis spectroscopic studies. The molecular structures of dinuclear (1) and polynuclear (2 and 3) complexes have been determined by the single crystal X-ray diffraction technique. The pyrazine-2,3-dicarboxylate acts as a bridging ligand through oxygen atom of carboxylate group and N atom of pyrazine ring and one oxygen atom of neighboring carboxylate. It links the Cu(II) ions to generate a distorted square pyramidal geometry forming a one-dimensional (1D) chain. Adjacent chains of 1 and 2 are then mutually linked via hydrogen bonding interactions, which are further assembled to form a two and three-dimensional network, respectively. The chains of complex 3 are further constructed to form three-dimensional framework by hydrogen bonding, C–H?π and ring?ring stacking interactions. In the complexes, Cu(II) ions have distorted square pyramidal geometry. Thermal analyses properties and thermal decomposition mechanism of complexes have been investigated by using thermal analyses techniques (TG, DTG and DTA).     

Hydrothermal synthesis of two copper helical coordination polymers with acentric three-dimensional framework constructing from mixed pyridine carboxylates

Two copper helical coordination polymers, [Cu(2-pc)(3-pc)]_n1 and [Cu(2-pc)(4-pc)]_n2 (2-pc=2-pyridine carboxylate, 3-pc=3-pyridine carboxylate, 4-pc=4-pyridine carboxylate) have been hydrothermally synthesized directly from pyridine carboxylic acids and copper nitrate. The crystal structure were determined by single-crystal X-ray diffraction with the following data: compound 1, orthorhombic, P2₁2₁2₁, a=6.591(3) Å, b=8.692(5) Å, c=20.548(9) Å, V=1177.2(9) Å³, Z=4; compound 2, orthorhombic, Pna2₁, a=21.160(10) Å, b=9.095(5) Å, c=6.401(3) Å, V=1231.9(11) Å³, Z=4. The acentric three-dimensional (3D) framework of 1 is constructed from right-handed helical Cu(2-pc) chains and left-handed Cu(3-pc) helices. As for 2, Cu(2-pc) helical chains, in which left- and right-handed helices are coexisting, and Cu(4-pc) zigzag chains combined together to form acentric 3D architecture of 2 as well. Additionally, besides general spectral characterization, we first introduce generalized 2D correlation spectroscopy to explore the coordination polymers and ascertain the stretching vibration location of carboxylate groups of compounds 1 and 2.     

Cyano-bridged 2D Cu(II)-Cr(III) coordination polymers: structural evidence for formation of a polymeric macrocyclic metallic compound

Two unique cyano-bridged 2D coordination polymers have been synthesized and characterized structurally and magnetically. The complexes contain two polyaza Cu(II) units and one novel macromolecular Cu(II) moiety, which have been synthesized via one-pot metal template condensation reactions involving ethylenediamine (en) and formaldehyde. Self-assembly of the polyaza Cu(II) mixture with [Cr(CN)(6)](3)(-) gave rise to two layered complexes. One complex contains unprecedented covalently linked polymeric Cu(II) chains and cyano-bridged Cu(II)(-)Cr(III) coordination chains, which are interwoven to form a novel layer. The other complex shows intriguing encapsulation of [Cr(CN)(6)](3)(-) anions. Intermetallic ferromagnetic coupling is operative within the bridged 2D layer. The magnetic susceptibilities of both complexes were simulated using approximate models.     

Assembly of trinuclear and tetranuclear building units of Cu2+ towards two 1D magnetic systems: synthesis and magneto-structural correlations

Two new 1D coordination polymers, [Cu(3)(μ(3)-OH)(ppk)(3)(μ-N(CN)(2))(OAc)](n) (1) and {[Cu(4)(pdmH)(2)(pdm)(2)(μ(2)-OH)(H(2)O)]·ClO(4)}(n) (2) based on two different blocking ligands phenyl-2-pyridylketoxime (ppk) and pyridine-2,6-dimethanol (pdmH(2)) have been synthesized and were characterized by X-ray single crystal structural analysis. In compound 1, the hydroxido-bridged trinuclear core, {Cu(3)(μ(3)-OH)(ppk)(3)(OAc)}, acts as secondary building units and are connected by the N(CN)(2)(-) anions resulting in a one dimensional (1D) coordination polymer. The 1D coordination chains undergo π-π interactions giving rise to a 3D supramolecular framework. In compound 2, tetrameric [Cu(4)(pdmH)(2)(pdm)(2)(H(2)O)](2+) cores are linked via hydroxido groups forming a zigzag 1D coordination chain where non-coordinated ClO(4)(-) ions are intercalated between the chains. Variable temperature magnetic susceptibility study of suggests that Cu(II) ions in the trinuclear Cu(3)(μ(3)-OH) cores are antiferromagnetically coupled with J = -459.7 cm(-1) and g = 2.11 and the trinuclear cores are further weakly coupled antiferromagnetically (zj' = -5.25 cm(-1)) through the N(CN)(2)(-) bridging ligand. Investigation of the magnetic properties of reveals that Cu(II) ions are coupled antiferromagnetically in the tetranuclear core with J = -27.1 cm(-1) and g = 2.17; the Cu(II)(4) building units are further coupled antiferromagnetically with zj' = -9.65 cm(-1). The experimental magnetic behaviours of 1 and 2 are correlated by first principle DFT calculations which provide a qualitative understanding of the origin of antiferromagnetic interactions in both cases.     

Hydrothermal synthesis and structure of a novel 3D framework based on ξ-octamolybdate chains: [Cu2(quinoxaline)2Mo4O13]n

An unprecedented three-dimensional (3D) polymer [Cu₂(quinoxaline)₂Mo₄O₁₃]_n, formed from ξ-octamolybdate chains as building units and pairs of 1D [Cu(quinoxaline)]_nⁿ⁺ polymeric chains as linkers, provides the first example of an extended higher dimensional structure based on octamolybdate chain. The basic building block of the octamolybdate chain included in the title compound is first reported to be constructed from ξ-isomer of octamolybdate unit.     

Synthesis and crystal structures of multidimensional coordination polymers based on W/Cu/S clusters with flexible imidazole ligands

Reactions of [WES3]2- (E = S, O) with CuX (X = NCS, CN, I) in the presence of bix (bix = 1,4-bis(imidazole-1-ylmethyl)benzene) in DMF or CH3CN resulted in the formation of two novel 2D --> 3D interpenetrating coordination polymers [S2W2S6Cu4(bix)2]n (1) and {[WS4Cu4(NCS)2(bix)3].CH3CN}n (2), a noninterpenetrating 3D polymer {[WS4Cu2(bix)].DMF}n (3), and two 2D sheet polymers [WS4Cu3(CN)(bix)]n (4) and {[OWS3Cu3(bix)2][I].DMF.2H2O}n (5), depending on the reaction temperature and the reagents used. Compound 1 contains a hexagonal prism of W2Cu4S6 cluster core, which serves as a 4-connecting node to link equivalent nodes via bix ligands, forming a 2D (4,4) net. In 2, a WCu4S4 core, which also acts as a 4-connecting node, connects the neighboring nodes either through single or double bix bridges, affording a different 2D (4,4) sheet. Inclined interpenetration occurs between two stacks of 2D sheets in the total structure of 1, while 2 involves a parallel interpenetration between the adjacent layers, both creating a 3D network. Compounds 1 and 2 represent the first examples of interpenetrating (4,4) frameworks with clusters as nodes and bidentate pyridyl-based ligands as linkers. Unlike 1 and 2, compound 3 has a noninterpenetrating 3D network, which is composed of the inorganic 1D (WS4Cu2)n chains linked by cis and trans bix ligands. Compound 4 features an inorganic 1D (WS4Cu3)n chain structure, which is linked by CN groups and bix ligands to form an infinite 2D network. Compound 5 is a 2D layer polymer with large inner cavities.